ANALYSIS AND DESIGN'OF CYCLOCONVERTER.FED
INDUCTION MOTOR DRIVE
KRISHNA KANT
DEPARTMENT OF ELECTRICAL ENGINEERING
THESIS SUBMITTED
IN FULFILMENT OF THE RE WIREMEN.TS :OF
THE DEGREE OF
DOCTOR OF PHILOSOPHY
TO THE
INDIAN INSTITUTE OF TECHNOLOGY, DE[,HI
JUNE, 198 2
Dedicated to
SHELLY AJ D SAUMITRA
CERTIFICATE
Certified that the dissertation entitled 'Analysis a 1d
Design of Cycloconverter-Fed Induction Motor Drive' , vhich
is being submitted by Shri Krishna Kant in fulfilment
for the award of the Degree of 'Doctor of Philosophy' in
Electrical Engineering of the Indian Institute of Technology,
Delhi is a record of the student's own work carried out by
him under our joint supervision and guidance. The matter
embodied in this dissertation has not been submitted for the
award of any other Degree or Diploma.
(J1. C1.atterjee)
DoledJune 30 -fti, I982.
(R. Arockiasamy)
ACKNO WLED GEMEN TS
The author wishes to express his profound gratitude to
Prof. Arockiasaiy for his invaluable guidance and inspiration
in carrying out the work. The author is greatly indebted to
Dr. J.K. Chatterjee for his unstinted help and encouragement
throughout the investigation.
Thanks are due to the authorities of the I.I.T. Delhi
for providing research facilities and to the supporting staff
of the Electrical Engineering Department for their whole hearted
cooperation.
Appreciation is extended to the Principal, Motilal Nehru
Regional Engineering College, Allahabi for sponsoring the
author, and to the Govt. of India for the award of the
scholarship under its Quality Improvement Programme.
The author wishes to thank MIs. R. Mulchandani, N.K.
Shards, and N.K. Jain for their valuable suggestions and
Mr. V.P. Gulati for patiently typing the thesis.
The author would like to thank Mrs. Veena Jain for the
help and encouragement provided by her in the later stages of
the work.
The author greatfully acknowledges the contribution of
his wife, Sadhana, who has been a constant source of encouragement, has silently endured all, and provided renewed motivation
during those black moments when it all seemed futile.
June, 1982
KRISHNA KANT
CONTENTS
PAGE
List of Principal Symbols
Summary
CHAP TER —1
xv
xxii
INTRODUCTION
1.1
General
..
1
1.2
DO Motor Vs. Induction Motor as
Traction Drive
..
2
_1.2.1Problems associated with
dc motors as Traction
drives
..
2
1.2.2Advantages of Induction
motor as Tr c t,ion drive
•.
4
Choice of Power Control Element
in ac Traction Using Three Phase
Induction Motor Drive
..
5
1.3
1.4
State of the Art in Cycloconverters
1.4.1Problemsassociatedwith
cycl oconver ter trigger
controller
1.5
6
..
8
1.4.2Cycloconverter operational
.,
pr9blems
9
1.4.3Analysis of Induction Motor
fed from non—sinusoidal,
variable frequency source ..
10
1.4.4AC traction system
..
12
Outline of Various Chapters
..
12
ii
CHAPTER-2
PRINCIPLE OF OPERATION AND
DESIGN OF SINGLE-PHASE TO THREEPHA,SE CYCLO CONVERTER
2.1
Introduction
..
15
2.2
Single Phase to Singhe Phase
Cycloconverter
,.
17
2.2.1Principle of Operation
..
17
2.2.2Voltage control and modulation..
21
2.2.3Trigger Requirements
..
23
2.2.4Load current
..
27
2.2.5Thyristor current and voltage ..
29
2.2.6Transformer current
..
36
Operation of Cycloconverter Under
Circulating Current Mode
..
42
2.3.1High Inductive Load
..
42
2.3.2Output frequency -non-integer
8tabmB1 tiple of the input
frequency
..
44
..
48
..
48
2.3.3.2Circulating current
inductor calculations..
49
2.3
2.3..3Operation of Cycloconverter
•
with circulating current
inductor
2.3.3.1Salient features of
circulating current
inductor
2.4
Single-Phase To Three-Phase
Cycloconverter
..
50
2.4.1Basic Principle of Operation
..
52
2.4.2Trigger Requirements
..
56
2.4.3Circuit Configurations
..
59
iii
2.5Single Phase To Three Phase
Cycloconverter Using Three
Transformers With Centre-Tapped
Secondary Winding
..
61
2.5.1Three Phase isolated load
2.5.2Three Phase neutral connected
..
65
Load
..
67
2.5.2.1Phase voltage
..
67
2.5.2.2Line voltage
2.5.2.3Load current
..
67
..
7:.
2.5.2.4Neutral current
..
73
,.
73
..
74
load with isolated neutral
..
74
2.5.3.1Neutral voltage
2.5.3.2Phase voltage
2.5.3.3Line voltage
2.5.3.4Load current
2.5.3.5Thyristor current and
..
74
..
77
,.
77
..
80
..
80
..
82
..
83
83
83
2.5.2.5Thyristor current and
voltage
2.5.2.6Transformer and input
currents
2.5.3Three Phase star connected
voltage
2.5.3.6Transformer and
input currents
2.5.4Three-phase delta
connected load
2.5.4.1Phase voltage
2.5.4.2Load current
..
,.
iv
2.6Single Phase to Three-Phase
Cycloconverter Using One
Transformer with Single CentreTapped Second ary Winding
2.6.1Transformer and input currents
2.6.1.1Three -phase neutral
connected load
..
85
..
92
..
92
2.6.1.2Three wire system of
loads(Star or Delta)
..
2.7Single Phase to Three Phase Cycloconverter Using one Transfor r with Three
Centre-Tapped Secondary Windings
..
2.8Single-Phase to Three Phase Cycloconverter Bridge Circuit
97
97
.. 100
2.8.1Three-phase isolated load
.. 102
2.8.2Three-phase Neutral connected
load
..
102
2.8.3Three Phase load with isolated
neutral
..
104
2.9Design Equations of the Single Phase
To Three Phase Cycloconverter
2.9.1Three-phase neutral connected
load
.. 106
.. 107
2.9.1.1Output voltage and
current
..
107
2.9.1.2Transformer and
input currents
..
110
..
112
2.9.1.3Transformer
r acing
2.9.1.4Thyristor rating
2.9.2Three Phase Star Connected
Load with Isolated Neutral
.. 113
..
114
2.9.2.1Output voltage and
current
..
114
2.9.2.2Transformer and
input currents
..
118
V
2.9.3
2.9.4
2.9.2.3
Transformer rating
.. 120
2.9.2.4
Thyristor rating
..
121
Three Phase delta connected
load
••
122
2.9.3.1
Output voltage and
current
.•
122
2.9.3.2
Transformer and input
currents
••
124
2.9.3.3
Trans former rating
..
126
2.9.3.4
Thyristor rating
..
127
RMS Value: General expressions
2.9.4.1
Transformer secondary
current
2.9.4.2
Thyristor current
2. 10Performance of the Cycl oconvertor
2.10.1 Resisitive load
2.10.2
Inductive load
2.10.3
Induction Motor load
2.11Conclusion
.. 128
••
129
130
..
132
..
135
•
135
137
137
CHAPTER-3TRIGGER CONTROLLER FOR SINGLE-PHASE
TO THREE-PHASE CYCLOCONVERTER
3.1Introduction
3.2Trigger Requirements
3.2.1 Single-phase converter
3.2.1.1Block diagram
3.2.2 Single-phase to single-phase
cycl oconver ter
3.2.2.1 Block diagram
140
.. 140
140
143
145
147
vi
3.2.3
3.3
Single-phase to three-phase
cycloconverter
Trigger Control Scher-1
3.3.1
Single-Phase to single-phase
cycloconverter
3.1.1.1Input stage
3.3.1.2Zero-crossing detector
3.3.1.3Pulse generator
3.3.1.4Synchronising network
3.3.1.5Counter
3.3.1.6Multiplexer
3.3.1.7Steering gates
3.3.1.8Output stage
3.3.2
151
..
153
..
153
153
154
154
..
..
..
.. 156
..
..
..
.,
Single-phase to three-phase
cycloconverter
..
3.3 2. 1Principle of operation
..
Discussion
..
156
156
157
157
Trigger Control Scheme-2
..
3.4.1
3.4.2
System description
..
159
161
162
162
167
Clock generator
..
167
3.4.2.1Input stage
3.4.2.2Sign detector
3.4.2.3Phase controller
3.4.2.4Synchronisation
ROM
.. 169
3.3.3
3.4
..
3.4.3
3.4.4
3.4.5
..
169
.. 169
..
170
..
176
Address Counter
..
177
Address comp .rator
.. 1?7
vii
3.4.6Output stage
.. 179
3.4.7Sensitivity to stray pulses.. 179
3.5
Experimental Results
.. 179
3.6
Conclusion
.. 181
CHAPTER -4
4.1
4.2
THEORETICAL INVESTIGATION OF PROBLEMS
ASSOCIATED WITH THE CYCLOCONVERTER
OPERATION ,LIMITATIONS I TD SOLUTIONS
Introduction
,
Presence of Circulating Current
4.2.1Resistive load
4.2.2Inductive load
4.2.2.1Inductive load with
low L/R ratio
4.2.2.2Inducti ve load with
large L/R ratio
4.3
.q
..
Time-domain Analysis of Cycloconverter
Feeding R-L Load 'Without CCI
183
184
186
., 186
.. 187
..
.. 192
4.3.1Model Formulation
.. 192
4.3.2General solution with a control .. 193
4.3.3Load current in the negative
half cycle
.. 194
4.3.3.1Conditions for short-
circuit free operation .. 196
4.4
4.3.4Results and discussion
.. 199
Analysis U.nder Inhibition Miode
..
4.4.1Results and discussion
4.5
201
.. 202
Effect of Circulating Current
Inductor
4.5.1Relationship between the
circulating current and the
CCI parameters
..
204
viii
Results and discussion
..
208
Effect of Free-Wheeling on the ShortCircuit Conditions
..
210
4.6.1
Formulation of the model
..
210
4.6.2
Solution
..
212
4.6.3
Results and discussion
..
213
..
215
..
217
Methods of Elimination of Short-circuit ..
218
4.5.2
4.6
4.7
Operation of tlECycloconverter With
Induction Motor Load
4.7.1
4.8
4.9
4.10
Effect of IM back emf on the
voltage waveform and on the
phenomenon of short-circuiting
4.8.1
Open loop blanking
..
220
4.8.2
Closed loop blanking
..
225
4.8.3
Load commutation
..
227
Circuit-1
..
229
4.8.3.2 Circuit-2
,.
232
Time-domain Analysis of Circuit-2
..
234
4.9.1
Formulation of the model
..
234
4.9.2
Results and discussion
..
238
..
239
Conclusion
CHAPTER-5INVESTIGATION OF SHORT CIRCUIT
PHENOMENON IN CYCLOCONUERTER-STATIC
LOAD SYSTEMS
5.1 Introduction
.. 241
5.2Experimental Set-up
.. 241
ix
5.3Cycloconverter with Inductive Load
5.3.1
5.3.2
CaseI: Low inductive load
Case II: High inductive load
5.3.2.1Observations
5.4Study
of the Effect of TimeConstant of the Circulating Current
Inductor on the Circulating Current
5.4.1
5.4.2
5.4.3
Experimental set-up
..
..
Effect of short circuit path
resistance Rt on free-wheeling/
short circuconditions
..
5.4.2.1Observations
..
Effect of free-wheeling on
the short circuit phenomenon
..
251
253
253
255
5.5.2.1Observations
257
.. 260
.. 261
.. 261
263
.. 266
Circuit behaviour at other
values of C
..
5.4.3.1Observations
5.5Elimination of Circulating Current
5.5.1
Experimental set-up
5.5.2
Operation with C=400 µF
5.5.3
243
.. 243
.. 243
.. 251
..
5.5.3.1Low C
5.5.3.2High C
5.6Conclusion
CHAPTER-6ANALYSIS OF SINGLE-PHASE TO THREEPHASE CYCLOCONVERTER FED INDUCTION
MO TOR
6.1 Introduction
..
268
.. 268
.. 270
270
S.
.. 272
x
6.2
Harmonic Analysis of the Cycloconverter Output Voltage
6.2.1
6.2.2
Fourier Coefficients of
cycloconverter phase voltages;
a =0
..
275
..
275
Fourier coefficients of cycloconverter phase voltages;
278
6.2.3.
Results and discussion
..
280
6.2.4
Fourier coefficients of line
voltage
..
285
6.2.4.1Results and discussion .. 285
6.3
Frequency Domain Analysis of Induction
TMIo t or
6.3.1
6.3.2
6.3.3
••
287
..
287
Frequency domain analysis of
induction motor fed from singl.ephas' to three-phase cycl o••
conver^ter
288
..
291
..
291
..
293
..
293
..
295
..
297
Frequency domain analysis of
three-phase induction motor
fed from a sinusoidal source
Resultsand discussion
6.3.3.1Torque-slip characteristics
6.3.3.2Power-slip characteristics
6.3.3.3Stator current-slip
characteristics
6.3.3.4 Power factor-slip
characteris tics
6.3.3.5Efficiency-slip
characteristics
xi
6.4Time-Domain Analysis of Three Phase
Induction Motor Fed from Single-
..
298
Mathematical model of singlephase to three-phase cycloconverter
..
6.4.2
Induction motor model
..
298
302
6.4.3
Method of solution
..
Phase to Three Phase Cycl oc onverter
6.4.1
6.4.3.3Machine emf
6.4.3.4Computer program
304
.. 305
.. 306
.. 307
.. 308
Results and discussion
..
312
..
...
312
319
..
319
..
322
326
6.4.3.1The current vector
6.4.3.2Air-gap torque
6.4.4
6.4.4.1Stator current
waveforms
6.4.4.2Machine emf
6.4.4.3Instantaneous air-gap
torque
6.4.4.4Stator terminal
voltage
6.5Conclusion
CHAPTER-7
..
EXPERIMENT.1 INVESTIGATION OF THE
PERFORMANCE OF CYCLO CONVERTERINDUCTION MOTOR SYSTEM
7.1
Introduction
..328
7.2
7.3
Experimental Set-up
..330
Stator Voltage and Current Waveforms
..331
7.3. iEffect of machine emf on the
cycloconverter phase voltages
7.3.2Effect of machine emf on
line voltages
..331
..333
xii
7.4
Machine emf and S hort Circuit
Condition
7.5
Effect of Capacitor on the Stator
Currenb and Voltage Waveforms
..
335
7.6
Performance Characteristics of the
Cycloconverter fed Induction Motor
(Without Capacitor)
..
Torque-speed characteristics
..
Power-speed characteristics
..
336
340
340
Stator current-speed
characteristics
..
340
7.6.4
Power factor-speed characteristics
..
343
7.6.5
Machine efficiency-speed
characteristics
..
343
..
343
7.6.1
7.6.2
7.6.3
7.7
7.8
335
Performance of the e.ycl oconverter
Feeding Induction Motor Load
7.7.1
Input current-speed characteristics
7.7.2
Input power factor-speed
characteristics
..
346
7.7.3
Cycloconverter efficiencyspeed characteristics
..
346
..
...
348
348
351
characteristics
..
351
7.8.4
Power factor-speed characteristics
..
351
7.8.5
Efficiency-speed characteristics
..
351
Effect of Capacitor on performance
of the Cycloconverter Fed Lnd uc ti on
Motor
7.8.1
7.8.2
7.8.3
Torque-speed characteristics
Power-speed characteristics
Stator: ourrent-speed
343
..
7.8 .6Effect
of variation of a on
torque-speed characteristics
7.9
..
353
..
356
..
356
..
356
..
356
..
358
..
358
for constant power operation
..
Operation From High Frequency Source
..
Conclusion
..
359
361
363
Effect of Capacitor on Performance of
the Cycloconverter Feeding Induction
Motor Load
7.9.1Comparison of cycloconverter
current, capacitor current and
the load current
7.9.2Input current-speed characteristics
7.9.3Input power factor-speed
characteris tics
7.9.4Cycloconverter efficiency-speed
characteristics
7.10
Torque-Speed Characteristics Under
Variable Frequency Operation
7.10.1Torque-speed characteristics
for constant torque operation
7.10.2Torque-speed characteristics
7.11
7.12
CHAPTER-8
CONCLUSIONS AND SUGGESTIONS FOR
FURTHER WORK
8.1
Introduction
..
8.2
8.3
Main conclusions
..
366
366
Suggestions for Further Work
..
370
,
373
REFERENCES
xiv
APPENDIXI :
Derivation of Average and
RMS Values of Single Phase
to Single Phase Cycloconverter
..379
APPENDIX II :
Mathematical Derivation of
Neutral Voltage
..380
APPENDIX III :
Derivation of Number of
Transformer Secondary Pulses
..381
APPENDIX IV
Component Specification
..383
APPENDIXV
Test Machine Specification
..384
APPENDIX VI :
Fourier Coefficients
..385
APPENDIX VII
Expressions for Frequency
Domain Machine Analysis
..387
APPENDIX VIII
Experimental Determination
of Machine Performance
..389